Bushfire risks posed by powerline failures are in the spotlight following last week's crisis in New South Wales, with officials at odds over whether electricity should be cut in extreme weather conditions.

The man responsible for electricity supply in South Australia says power would be turned off if his state was confronted with conditions like those prevailing on Black Saturday in Victoria.

It is controversial, but Mr Duffy has told Four Corners the strategy has been used successfully on a number of occasions.

There are others, however, who believe the benefits of leaving the power on outweigh the risks of it starting a bushfire.

In the wake of the NSW bushfire crisis, Four Corners has examined almost four decades worth of evidence into the cause and impact of major bushfires.

Some of the most catastrophic bushfires in Australia's history have been started by powerline failure.

It is believed the most devastating fires in NSW last week began as a result of damaged powerlines.

In Victoria's Murrindindi fire in 2009, which led to 40 deaths on Black Saturday, police initially focused their investigation on an alleged arsonist.

However, after abandoning that line of inquiry, a case is now being made that a fallen powerline ignited the blaze.

Law firm Maurice Blackburn is representing victims of the Murrindindi fire in a class action against power company SP Ausnet. The company rejects accusations its wire caused the fire.

If proven, it means 93 per cent of the deaths on Black Saturday - Australia's worst bushfire disaster - were caused by fires started by powerlines.

Confronted with these facts, the head of Victoria's power industry safety regulator, Paul Fearon, says he would still not recommend turning power off to high-risk areas in his state, even if the conditions replicated Black Saturday.

"If I was faced with exactly the same conditions, I would not be recommending the power be turned off," he said.

Both NSW and Victorian authorities believe the benefits of leaving the power on outweigh the risks. They warn that turning power off could cost lives.

Four Corners found that despite several inquiries identifying the danger posed by powerlines, they continue to ignite destructive fires.

In the wake of successive bushfire disasters, attention has centred on arsonists, bush-clearing practices and fire-fighting tactics, including the stay-or-go policy.

The issue of powerlines has not been at the centre of public debate.

The program also found power companies have known since 1974 that their lines can cause fires.